Formation of metal oxide gate dielectric

ABSTRACT

Formation of a gate dielectric includes forming a metal oxide on at least a portion of the surface of the substrate assembly by electron beam evaporation. An ion beam is generated using an inert gas to provide inert gas ions for compacting the metal oxide during formation thereof.

This is a division of application Ser. No. 09/779,959, filed Feb. 9,2001, now U.S. Pat. No. 6,495,436, which is incorporated herein byreference.

FIELD OF THE INVENTION

This invention relates to semiconductor fabrication methods andapparatus for implementing such methods. More particularly, the presentinvention relates to metal oxide gate structures for semiconductordevices, e.g., MOSFET devices, memory devices, etc., and otherstructures including metal oxide dielectric material.

BACKGROUND OF THE INVENTION

Semiconductor devices such as field effect transistors are commonly usedin the electronics industry. Such devices may be formed with extremelysmall dimensions, such that thousands or even millions of these devicesmay be formed on a single crystal silicon substrate or “chip” andinterconnected to perform useful functions in an integrated circuit suchas a microprocessor, a memory device, etc. For example, metal oxidesemiconductor (MOS) devices are widely used in memory devices thatcomprise an array of memory cells that include field effect transistorsand capacitive structures.

Although transistor design and fabrication are generally complex, asimplified field effect transistor is described below. In such a fieldeffect transistor, a portion of a substrate near the surface isdesignated as a channel of the transistor. The channel is electricallyconnected to a source and a drain such that when a voltage differenceexists between the source and the drain, current will tend to flowthrough the channel. The semiconducting characteristics of the channelare altered such that its resistivity may be controlled by the voltageapplied to a gate, which generally includes a conductive layer or gateelectrode overlying the channel. By changing the voltage on the gate,more or less current can be made to flow through the channel. The gateelectrode and the channel are separated by a gate dielectric. Generally,the gate dielectric is insulating, such that between the gate andchannel little or no current flows during operation, although tunnelingcurrents observed within certain dielectrics. The gate dielectric allowsthe gate voltage to induce an electric field in the channel.

Generally, integrated circuit performance may be enhanced by scaling. Inother words, performance and density are enhanced by decreasing the sizeof the individual semiconductor devices on the chip. This has beenaccomplished by decreasing the thickness of the gate dielectric, thusbringing the gate in closer proximity to the channel. As modern silicondevice size becomes smaller or has been scaled to smaller and smallerdimensions, with a corresponding size reduction of the gate length ofMOS devices, the gate dielectric thickness has continued to decrease,for example, to less than 2 nm (20 Å) and as thin as 1 nm (10 Å).

However, the most commonly used gate dielectric material, silicondioxide, exhibits high leakage current density in this thickness rangebecause of direct band-to-band tunneling current or Fowler-Nordheimtunneling current. Further, because such silicon dioxide layers areformed from a few layers of atoms, complex process control is requiredto repeatably produce such silicon dioxide layers. Further, uniformityof coverage is also critical because device parameters may changedramatically based on the presence or absence of even a single monolayerof dielectric material. Because of the limitations of silicon dioxide,alternative high dielectric constant (K) films such as TiO₂, Ta₂O₅,HfO₂, and other high dielectric films have received a lot of interest assubstitutions for very thin silicon dioxide gate dielectrics. Suchalternate dielectric materials can be formed in a thicker layer thansilicon dioxide and yet still produce the same field effect performance.Such performance is often expressed as “equivalent oxide thickness.” Inother words, although the alternate material layer may be thick, it hasthe equivalent effect of a much thinner layer of silicon dioxide. Mostof the interest in alternate materials for silicon dioxide have employedthe use of metal oxides.

Various methods have been described for the formation of metal oxides,e.g., formation of metal oxide gate dielectrics. For example, inHaraguchi et al., “A TiO₂ Gate Insulator of a 1-nm Equivalent OxideThickness Deposited by Electron-Beam Evaporation,” Extended Abstracts of1999 International Conference on Solid State Devices and Materials, pps.376-377 (1999), fabrication of thin dielectric films by electron beamevaporation was described. As described in Haraguchi et al., one of themore common methods of forming metal oxide films, e.g., titanium dioxide(TiO₂), is by chemical vapor deposition. However, for example,impurities such as carbon and chlorine originating from titaniumprecursors in such chemical vapor deposition processes may causeundesirable influence on the TiO₂ film properties. To achieve thepreparation of high purity TiO₂ films, electron beam evaporation (asdescribed in Haraguchi et al.) has been used instead of chemical vapordeposition.

For example, as described in Haraguchi et al., electron beam evaporationfor forming metal oxides was performed in the ambient of ozone plasmaminimizing the effect of oxygen depletion, resulting in pure TiO₂ films.Further, by optimizing TiO₂ deposition thickness and TiO₂ annealingconditions, TiO₂ films with 1 nm equivalent oxide thickness which showedlow leakage current and interface trap density were realized.

However, even though electron beam evaporation methods have been foundto produce metal oxides which show low leakage current and have suitableequivalent oxide thickness, optimization of such film formationprocesses are necessary. The optical properties for most vacuumevaporated thin films change when the films are exposed to moisture, andthey are unstable in air since the properties are dependent on therelative humidity. Such properties are attributed to microstructure ofthe films, which have been reported to include approximately cylindricalcolumns several tens of nanometers in diameter with voids between them.As a result, the density of the films is less than that of the bulkmaterial. Upon contact with the moisture, the internal surfaces of thecolumns adsorb a monolayer of water. On exposure to a humid atmosphere,the voids act as capillaries and fill with water, upon bringing therelative humidity above a certain threshold, which depends upon thediameter of the pores. Consequently, the refractive indices of the filmswhen deposited are less than those of the bulk material and change whenthe film is exposed to a humid atmosphere. The extent of the change isdependent upon the relative humidity. Typical packing densities for suchfilms have been found to be between 0.75 to 1.0.

Higher packing densities for films and, hence, increased stability werereported to be achieved as described in an article by Martin et al.,“Ion-beam-assisted deposition of thin films,” Applied Optics, Vol. 22,No. 1 (Jan. 1, 1983), where the adatoms had greater mobility on thesubstrate surface. The article indicates they can be produced by heatinga substrate or by increasing the energy of the arriving atoms ormolecules as occurs in sputtering or ion beam deposition. Additionalactivation energy can be added to the growing film if it is bombardedwith low energy ions during deposition, as reported therein.

In addition, an article by Souche et al., entitled “Visible and infraredellipsometry study of ion assisted SiO₂ films,” Thin Solid Films, Vol.313-314, pps. 676-681 (1998), described the study of oxygen ion-assistedsilica thin films by means of in situ visible spectroscopic ellipsometryand infrared spectroscopic ellipsometry in air. The article discussesthe transition from porous evaporated films to compact films, withemphasis on compaction of silicon dioxide films by ion-assisteddeposition.

Further, ion-assisted deposition of silver thin films was described inan article by Lee et al., entitled “Ion-assisted deposition of silverthin films,” Thin Solid Films, Vol. 359, pps. 95-97 (2000). The articledescribes silver films deposited with ion bombardment which are moredurable in a humid environment and maintain a higher value ofreflectance over time than those deposited without ion bombardment. Theeffects of ion bombardment was found to reduce the surface roughness andincrease the film density. Further, the hardness of the films increased.Yet further, the article described the finding that lattice spacingincreased.

SUMMARY OF THE INVENTION

The present invention optimizes the formation of high dielectric filmsusing electron beam evaporation. For example, the present inventionoptimizes such evaporation processes with the use of high purity sourcematerials, use of ion beam bombardment techniques, use of an ozoneenvironment, etc.

A method for use in fabrication of a gate structure according to thepresent invention includes providing a substrate assembly having asurface located in a vacuum chamber and forming a gate dielectric on thesurface. The formation of the gate dielectric comprises forming a metaloxide on at least a portion of the surface of the substrate assembly byelectron beam evaporation and generating an ion beam using an inert gasto provide inert gas ions for contacting the metal oxide duringformation thereof.

In one embodiment of the method, an environment including oxygen may beprovided in the vacuum chamber. The formation of the metal oxide occursin the oxygen environment. For example, the environment provided may bean ozone environment in the vacuum chamber and/or an ozonizer structureproximate the substrate assembly surface may be used to direct ozonetowards the substrate assembly surface.

In other embodiments of the method, the method may include heating thesubstrate assembly as the metal oxide is formed and/or delaying contactof the inert gas ions with the metal oxide until at least a monolayer ofmetal oxide is formed.

A method for use in fabrication of a gate structure according to thepresent invention includes providing a substrate assembly having asurface located in a vacuum chamber and forming a gate dielectric on thesurface. The formation of the gate dielectric includes providing anenvironment including ozone in the vacuum chamber, forming TiO₂ on atleast a portion of the surface of the substrate assembly by electronbeam evaporation in the environment including ozone, and generating anion beam using an inert gas to provide inert gas ions for contacting theTiO₂ during formation thereof.

In one embodiment of the method, forming TiO₂ on at least the portion ofthe surface of the substrate assembly by electron beam evaporationincludes directing an electron beam at a high purity TiO₂ sourcematerial. The high purity source material has a purity of TiO₂ that isabout 99.999% or greater.

In another embodiment of the method, forming TiO₂ on at least theportion of the surface of the substrate assembly by electron beamevaporation includes directing an electron beam at the high purity TiO₂source material such that a deposition rate for TiO₂ on the surface ofthe substrate assembly is about 0.1 nm/second to about 0.2 nm/second.

In other embodiments of the method, forming TiO₂ on at least a portionof the surface of the substrate assembly may include forming TiO₂directly on at least a silicon containing portion of the surface of thesubstrate assembly and/or the method may include forming a conductivegate electrode on the gate dielectric.

Another method for forming a high dielectric constant metal oxide in thefabrication of integrated circuits is described. The method includesproviding a substrate assembly having a surface located in a vacuumchamber and forming a metal oxide on at least a portion of the surfaceof the substrate assembly by evaporating a metal oxide source materialusing an electron beam. Contact of inert ions with the metal oxide isprovided during formation thereof.

In other embodiments of the method, the metal oxide may be at least aportion of a gate dielectric or the metal oxide may be at least aportion of a dielectric material for a capacitor.

A system for use in the fabrication of a gate structure according to thepresent invention includes a vacuum chamber including a substrateassembly holder adapted to hold a substrate assembly having a surfaceand an ozonizer apparatus. The ozonizer apparatus includes an ozonesource and an ozonizer structure proximate the surface of the substrateassembly in the vacuum chamber. The ozonizer structure has openingsadapted to direct ozone towards the surface of the substrate assembly.The system further includes an evaporation apparatus. The evaporationapparatus includes a metal oxide source and an electron beam generationdevice operable to generate an electron beam that impinges on the metaloxide source to evaporate metal oxide of the metal oxide source forformation of metal oxide on the surface of the substrate assembly. Yetfurther, the system includes an ion beam apparatus. The ion beamapparatus includes an inert gas source operable to provide an inert gasand an ion gun operable to generate an ion beam using the inert gas anddirecting the ion beam for contact at the surface of the substrateassembly.

In various embodiments of the system, the metal oxide source may includea high purity source material (e.g., a purity that is about 99.999% orgreater); the metal oxide source may include material selected from thegroup consisting of TiO₂, Y₂O₃, Al₂O₃, ZrO₂, HfO₂, Y₂O₃—ZrO₂, ZrSiO₄,LaAlO₃, and MgAl₂O₄; and/or apparatus may include a controller operableto delay generation of the ion beam until at least a monolayer of metaloxide is formed using the evaporation apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a structure including a metal oxide formed according to thepresent invention.

FIGS. 2A-2C show a process for forming a gate using a high dielectricconstant metal oxide gate dielectric formed according to the presentinvention.

FIG. 3 shows a general diagram of an apparatus for formation of highdielectric constant metal oxide according to the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention shall be described with reference to FIGS. 1-3.FIG. 1 and FIGS. 2A-2C shall be used to describe the process of formingmetal oxide according to the present invention, e.g., metal oxide gatedielectric, while the apparatus for forming a metal oxide shall bedescribed with reference to FIG. 3. With the description as providedbelow, it is readily apparent to one skilled in the art that the variousprocesses and the steps thereof described with reference to the figuresmay be utilized in various configurations and/or applications. Forexample, the present invention may be used in the formation of gatedielectrics, dielectrics for capacitors, or for any other applicationsrequiring a dielectric or insulating material. Further, for example, thepresent invention may be particularly beneficial in the fabrication ofgate dielectrics for transistor applications in memory devices, e.g.,DRAMs.

In this application, “semiconductor substrate” refers to the basesemiconductor layer, e.g., the lowest layer of silicon material in awafer or a silicon layer deposited on another material such as siliconon sapphire. The term “semiconductor substrate assembly” refers to thesemiconductor substrate or the semiconductor substrate having one ormore layers or structures formed thereon or regions formed therein. Whenreference is made to a substrate assembly in the following description,various process steps may have been previously utilized to formregions/junctions in the semiconductor substrate thereof. It should beapparent that scaling in the figures does not represent precisedimensions of the various elements illustrated therein.

Further, as used herein, “high dielectric constant” refers to adielectric constant greater than 3, and preferably greater than 10. Alsoas used herein, the term “deposition temperature” will typically referto the surface temperature of the substrate assembly or layer upon whicha material is being deposited; the term “flow rate” as used herein inconnection with gas flow rates will typically refer to the gas flow rateprovided to a particular component or portion of a system according tothe present invention; and the term “deposition pressure” will typicallyrefer to the pressure within the chamber wherein the substrate assemblyor layer upon which a material is being deposited is positioned.

FIG. 1 shows a structure 10 including a substrate assembly 12 upon whicha metal oxide 14 is formed. The substrate assembly 12 may be either asemiconductor substrate or a semiconductor substrate having one or morelayers, structures, or regions formed thereon or therein. For example,in one preferred embodiment wherein the metal oxide 14 is used to form agate dielectric as shown in FIGS. 2A-2C, the substrate assembly 12 is asilicon substrate.

The metal oxide 14 may be any high dielectric metal oxide. Preferably,the metal oxide includes at least one of TiO₂, Y₂O₃, Al₂O₃, ZrO₂, HfO₂,Y₂O₃—ZrO₂, ZrSiO₄, LaAlO₃, or MgAl₂O₄. More preferably, the metal oxideis TiO₂. Although the present invention may be beneficial in forming anyof the high dielectric constant materials listed above, for simplicitypurposes, and preferably, the remainder of the description below isprovided with respect to the formation of TiO₂, e.g., formation of TiO₂for a gate dielectric.

In addition, the present invention will primarily be described withreference to the formation of a metal oxide for a gate dielectric asdescribed with reference to FIGS. 2A-2C. However, the metal oxide may beused for any other application as shown generally with reference to FIG.1 wherein the substrate assembly 12 may be either a semiconductorsubstrate or, for example, a semiconductor substrate assembly includingan electrode region upon which a metal oxide is formed, e.g., acapacitor application.

As shown in FIGS. 2A-2C, a simplified flow process for forming a gate 25(see FIG. 2C) is shown. In FIG. 2A, a device structure 20 is fabricatedin accordance with conventional processing techniques prior to theformation of metal oxide 26 on the device structure 20. As such, priorto the formation of the metal oxide 26, the device structure 20 includesfield oxide regions 24 and active areas, i.e., those regions of asubstrate 22 not covered by field oxide regions 24. Suitably dopedsource/drain regions 32-33, as shown in FIG. 2C, are formed as known toone skilled in the art.

As shown in FIG. 2A, metal oxide 26 is formed over the field oxideregions 24 and semiconductor substrate 22 as described further below. Inaddition, as shown in FIG. 2B, various other layers 28-30 may be used toform a conductive gate electrode relative to the gate dielectric 26. Forexample, as shown in FIG. 2B, three layers 28-30 are formed andthereafter, as shown in FIG. 2C, the gate dielectric and the multipleconductive layers 28-30 are patterned resulting in gate dielectric 36and gate electrode layers 38-40 to form the gate 25. Various techniquesfor patterning the layers, e.g., removing unmasked regions, are know tothose skilled in the art and the present invention is not limited to anyparticular technique.

As known to one skilled in the art, in a field effect transistor, aportion of the substrate 22 near the surface is designated as a channel23 during processing. Channel 23 is electrically connected tosource/drain 32-33 such that when a voltage difference exists betweenthe source/drain, current will tend to flow through the channel 23. Thesemiconducting characteristics of channel. 23 are altered such that itsresistivity may be controlled by the voltage applied to gate 25. Thus,by changing the voltage on gate 25, more or less current can be made toflow through channel 23. The conductive gate components 38-40 andchannel 23 are separated by gate dielectric 36. The metal oxide gatedielectric 36 is insulative such that between the conductive gatecomponents 38-40 and channel 23 little or no current flows duringoperation. However, the metal oxide gate dielectric 36 allows the gatevoltage to induce an electric field in channel 23. After formation ofthe gate 25, various processing techniques, such as, for example,metalization techniques used for providing electrical connection to thesource/drain 32, 33 and the gate 25, are used to complete formation of,for example, the complete transistor device, interconnect levels, memorydevice structures including capacitive structures formed thereafter,etc.

It will be readily apparent that the present invention is focused on theformation of the metal oxide gate dielectric 36 and the other stepsutilized therewith may be those known to one skilled in the art. Forexample, various manners of doping the source and drain may be used, oneor more layers may be used for formation of the conductive gateelectrode portion of gate 25 (e.g., polycide structures, silicidelayers, etc.), various silicidation processes or salicidation may beused for metalization of the various regions, etc., without limiting theprocess of forming the metal oxide gate electrode 36.

For simplicity purposes, the remainder of the description below shall belimited to the formation of the metal oxide 26, with the metal oxide 26preferably being TiO₂. Generally, the present invention forms TiO₂ byelectron beam evaporation from a TiO₂ source, e.g., high purity TiO₂slug, in a vacuum chamber in the presence of an ion beam. Preferably,the TiO₂ is formed on a heated substrate assembly, and also in thepresence of an oxygen atmosphere, e.g., O₂ or ozone. The presence of anion beam during deposition of the metal oxide by evaporation enhancesthe packing density and makes the metal oxide more reliable in terms ofdielectric breakdown and reducing tunneling current. The metal oxidefilm produced provides an adequate equivalent oxide thickness, with themetal oxide thickness of the material formed being in the range of about50 Å to about 500 Å. Since tunneling currents are exponential functionsof electric fields, the thicker films of TiO₂ will result in much lowerelectric fields and insignificant tunneling currents when compared tothe use of silicon dioxide.

The formation of TiO₂ according to the present invention shall befurther described with reference to the metal oxide evaporation system50 shown in FIG. 3.

The metal oxide evaporation system 50 includes a vacuum chamber 52 inwhich a substrate assembly, e.g., wafer 62, is positioned and held bysubstrate holder 64. The substrate assembly, e.g., wafer 62, may be anysubstrate assembly as previously described herein and it may be held inthe vacuum chamber 52 by any suitable substrate holder, e.g., electricalor mechanical coupling structures.

The metal oxide evaporation system 50 further includes a heaterapparatus 66 for heating the substrate assembly 62 as the metal oxide 26is formed. The evaporation system 50 further includes electron beamevaporation apparatus 74 in which a stream of electrons is acceleratedto a high energy and directed at source material 106 to be evaporated.The electron stream melts and evaporates the material 106 for depositionof the metal oxide on surface 63 of substrate assembly 62.

In addition, the evaporation system 50 includes ion beam apparatus 78and ozonizer apparatus 76. The ion beam apparatus 78 provides for thegeneration of an ion beam using an inert gas to provide inert gas ionsfor contacting, e.g., such as for compacting, the metal oxide duringformation thereof. The ozonizer apparatus 76 compensates for the loss ofoxygen in the deposited TiO₂.

Further, included in the metal oxide evaporation system 50, is a shutter80, e.g., a mechanical shutter, located between the substrate assembly62 and electron beam evaporation apparatus 74. In addition, a monitoringapparatus 82, e.g., a quartz crystal thickness monitor, is furtherprovided as described below.

The heater apparatus 66 may be any apparatus suitable for heating thesubstrate assembly 62. Preferably, for the formation of TiO₂, thesubstrate assembly temperature is between about 100° C. to about 150° C.As shown in FIG. 3, one suitable embodiment of the heater apparatus 66includes a heating element 68 surrounded by a heat reflector 70 forreflecting heat to the substrate assembly 62.

The electron beam evaporation apparatus 74 generally includes anelectron beam gun 104 for generating an electron beam 102 directed at anevaporant source 106 to melt evaporant material thereof. Generally, theelectron beam 102 can melt and evaporate material of source 106,provided the beam 102 can supply energy to the evaporant at an equal orgreater rate than the rate at which heat is lost as the material is heldat high temperature. Electron beam guns are available that supply up to10 kilowatts of highly concentrated electron beam power for evaporationapplications. Very high film deposition rates can thereby be attained asa result of the high power available. The electron beam evaporationapparatus 74 further includes a controller 108, shown generally in FIG.3, for controlling operation of the electron gun 104 and evaporationprocess. Preferably, the controller 108 adjusts the electron gun powersuch that the gun will yield a deposition rate of about 0.1 nm/sec to1.0 nm/sec when used in forming metal oxides according to the presentinvention, particularly with respect to TiO₂.

The beam energy is concentrated on the surface of the evaporant source106, and thus, a molten region can be supported by a cooled structure.The target material, or evaporant source itself, typically provides asolid layer that separates the molten portion of the evaporant materialfrom a holder, e.g., a crucible, that is cooled. This eliminates theproblem of reaction with or dissolution of the holder by the melt andallows highly pure films to be deposited. This holder is typicallycopper, which has a high melting temperature.

Preferably, the evaporant source 106 includes high purity metal oxide.As used herein, high purity metal oxide refers to a metal oxide having apurity that is about 99.999% or greater. For example, in one preferredembodiment, the evaporant source 106 includes TiO₂ that is greater thanabout 99.999% pure.

The electron beam gun 104 is generally a self-accelerating, 270° beamgun that is generally a standard design and commonly available. In suchguns, a magnetic field simultaneously bends the beam 102 to 270° andfocuses the beam on the evaporant source 106. The electron emissionsurface is hidden from the evaporating source 106, and the substratesare also protected from contamination by material evaporating from theheated filament of the gun. Movement of the beam 102, which allows theevaporant source to be scanned, may be accomplished by electromagneticdeflection. This avoids the problem of non-uniform deposition that maybe caused by the formation of a cavity in the molten evaporant source ifthe beam 102 were stationary. Although various preferred parameters aregiven for the electron beam gun 104 as described above, any suitableelectron beam gun may be used according to the present invention, e.g.,a Temescal electron beam gun).

The ion beam apparatus 78 which provides for bombardment of thesubstrate assembly surface 63 uniformly during metal oxide formationincludes an ion gun 120, an ion gas source 122, and an ion beamcontroller 124. The ion beam apparatus 78 provides for compacting of themetal oxide formed on the surface 63 of substrate assembly 62.

The ion gas source 122 may be any inert gas. As referred to herein,inert means any gas that is nonreactive with the materials beingdeposited. Preferably, the ion gas source includes at least one ofargon, xenon, and krypton. More preferably, the ion gas source is argon.

The ion gun 120 may be any suitable type of ion gun that provides forcompaction of the metal oxide being formed, such as a Kaufman-type iongun. Ion guns are commonly available, such as those available fromApplied Materials, Inc. Preferably, the ion beam incident angle (α) iswithin the range of +40 degrees to about −40 degrees relative to thesurface 63 as shown in FIG. 3. Further preferably, the ion beam gun 120is an ion gun with a fairly large diameter. Preferably, the diameter isin the range of 7.6 cm to 10 cm. Yet further, the ion gun is preferablya filament-type gun which uses a hot filament to ionize the gas from gassource 122. A filament-type ion gun is preferred over a cold catheterdischarge ion gun.

The ion beam gun 120 is controlled by controller 124 to produce an ionbeam density for bombardment of the material being formed on surface 63.Preferably, the ion beam density is in the range of about 0.5 ma/cm² toabout 1.0 ma/cm². An ion beam density in this range is generallyrequired to obtain a suitable degree of compaction by the bombardment ofions on substrate assembly surface 63 as the metal oxide is beingformed.

In addition to the use of the electron beam evaporation apparatus 74 andthe ion beam apparatus 78 in the formation of metal oxide on surface 63of substrate assembly 62 mounted in the reaction chamber 52, theozonizer apparatus 76 provides the necessary oxygen to compensate forany loss of oxygen in the evaporated metal oxide. The ozonizer apparatus76, as shown in FIG. 3, includes the ozonizer structure 132 forproviding ozone into the vacuum chamber 52 from the ozone source 130under the control of controller 136. Although the vacuum chamber 52 maybe flooded with oxygen, e.g., O₂ or O₃, the ozonizer structure 132 ispreferably adapted to direct ozone towards the surface 63 of thesubstrate assembly 62 upon which the metal oxide is deposited. Thismaintains the ozone in the region of formation of the metal oxide on thesurface 63 and provides for uniform distribution of ozone in thisregion.

Preferably, according to the present invention as shown in FIG. 3, theozonizer structure 132 includes a ring 133 with center axis 81therethrough. The ring 133 has a plurality of openings 135 adapted todirect ozone towards the surface 63 of the substrate assembly 62. Thering 133 having the openings 135 enhance the uniform distribution ofozone in the region of the surface 63. The ozonizer ring 133 ispositioned generally parallel with the substrate assembly 62, e.g.,semiconductor wafer, with the openings 135 adapted for directing ozonetowards the surface 63. The ozonizer ring 133 is generally of a sizethat does not inhibit the ion beam generated by the ion beam gun 120from bombardment of the surface 63 as the metal oxide is formed.

The metal oxide evaporation system 50 further includes a shutter 80,e.g., a mechanical shutter, located between the substrate assembly 62and the electron beam gun 104 in the vacuum chamber 52. The shutter 80is employed to prevent contaminants absorbed on the evaporant sourcesurface from being incorporated into deposited metal oxide. In otherwords, if the vacuum chamber and the evaporant source are exposed toambient conditions in the loading and unloading of substrate assemblies,e.g.,wafers, some contamination may occur on the evaporant source.Therefore, when the source is initially heated, such surfacecontaminants may vaporize together with source material and, as such,contaminate the metal oxide formed on surface 63. By interposing theshutter between the evaporant source 106 and the surface 63 andpostponing formation of the metal oxide until the evaporant source 106is sufficiently clean, the purity of the formed metal oxide can beenhanced.

Further included in the vacuum chamber 52 is monitoring apparatus 82which monitors the metal oxide thickness being formed on substratesurface 63. Further, incorporation of oxygen in the film may also bemonitored. Various types of monitoring apparatus 82 may be used, such asa quartz crystal thickness monitor or an oxygen pressure monitor formonitoring oxygen incorporation. Such monitoring may provide informationto one or more of the controllers of the system 50. For example, theconcentration of ozone in the vacuum chamber 52 may be controlled bymonitoring the oxygen content in the film using monitoring apparatus 82and adjusting, via controller 136, the ozone in the region proximate thesurface 63 of substrate assembly 62. Likewise, the deposition rate maybe adjusted under control of controller 108 as a result of informationavailable from monitoring apparatus 82, concerning the thickness of themetal oxide being formed on surface 63. Although several monitoringdevices are described above, the present invention is not limited tothose listed.

Generally, as shown in FIG. 3, the vacuum chamber 52 includes anelongated chamber space extending between a first end 160 and a secondend 161 along axis 81. The electron beam gun 104 is centrally locatedtoward the bottom or second end 161 of the vacuum chamber 52. Thesubstrate assembly holder 64 which holds the substrate assembly 62 issurrounded by the heater apparatus 66 at the first end 160 of the vacuumchamber 52. Proximate the substrate assembly 62 is the ozonizer ring 133with the small openings 135 directed to the substrate assembly 62 foruniform distribution of ozone, particularly to compensate for loss ofoxygen in an evaporated TiO₂ film. The shutter 80 is located between thesubstrate assembly 62 and the ozonizer ring 133. The ion beam gun 120 islocated generally towards the substrate assembly 62 relative to the ionelectron beam gun 104 and slightly off axis from the center location ofthe electron beam gun 104.

Generally, the method of forming metal oxide using, for example, theevaporation system 50 described with reference to FIG. 3 shall bedescribed below. The description of the formation method below isprovided with respect to TiO₂ formation, however, the general conceptsemployed in the formation method are applicable to the other highdielectric constant materials as listed previously herein.

The vacuum chamber 52 is pumped down to a pressure in the range of about2×10⁻⁶ torr to about 8×10⁻⁶ torr as generally represented by arrow 54.The heater apparatus 66 is controlled to provide a depositiontemperature of about 100° C. to about 150° C. The evaporant source 106is a high purity TiO₂ slug.

The controller 108 initializes the evaporation process. Although the ionbeam gun 120 may be initiated by controller 124 simultaneously with theelectron beam evaporation apparatus 74, preferably, the introduction ofthe ion beam used to bombard the substrate assembly surface 63 duringthe metal oxide formation from the evaporation of the evaporant source106 is delayed for a predetermined period of time to allow deposition ofat least one monolayer of the metal oxide, e.g., TiO₂. This providesprotection in the case of a silicon substrate surface 63 from possibledamage caused by the ion beam bombardment. Preferably, the electron beamgun power is adjusted such that the gun will yield a deposition rate ofabout 0.1 nm/sec to 1.0 nm/sec.

Further, preferably, the ion beam apparatus 78 provides an argon ionbeam density in the range of about 0.5 ma/cm² to 1 ma/cm². However, asdescribed above, preferably, the ion beam is delayed followinginitialization of the evaporation apparatus for a period of time, e.g.,approximately 1-2 seconds, to allow deposition of at least one monolayerof TiO₂.

Further, upon initialization of the evaporation apparatus 74, apre-evaporation phase is completed during which shutter 80 is closed,preventing formation of metal oxide on surface 63. During thepre-evaporation phase, outgasses resulting from evaporation during thepre-evaporation phase are exhausted, as is generally represented byarrow 55. As such, contaminants which potentially may contaminate themetal oxide film being formed are removed during the pre-evaporationphase.

Following the pre-evaporation phase, the shutter 80 is opened to allowformation of the metal oxide on surface 63. Preferably, only after atleast a monolayer of TiO₂ is formed is the argon beam initiated toprovide for compaction during the remaining formation of the TiO₂.

During formation of the TiO₂ on surface 63, the partial pressure ofozone provided by the ozonizer apparatus 76 in the vacuum chamber 52 isin the range of about 2×10⁻⁵ torr about 8×10⁻⁵ torr. The optimumparameters for the ozone in the region proximate the substrate assembly62 is or may be determined by monitoring the oxygen content in the metaloxide being formed as represented generally by the monitoring apparatus82.

Use of the ion bombardment of the substrate assembly surface 63uniformly during metal oxide formation will provide a desirable compactmetal oxide. Preferably, in the case of a TiO₂ gate dielectric, the TiO₂thickness is in the range as described previously herein with referenceto FIGS. 2A-2C. Typical packing densities for the metal oxide arepreferably in the range of about 0.9 to about 1.0. In other words, theratio of a metal oxide film deposited without the use of ion bombardmentversus a metal oxide film deposited using ion bombardment is in therange of about 0.9 to about 1.0.

One skilled in the art will recognize that various commercial componentssuch as electron beam guns and ion beam guns are available for use andmodification according to the present invention. All patents and/orreferences cited herein are incorporated in their entirety as if eachwere incorporated separately. This invention has been described withreference to illustrative embodiments and is not to be construed in alimiting sense. Various modifications of the illustrative embodiments,as well as additional embodiments of the invention, will be apparent topersons skilled in the art upon reference to this description. Aspreviously indicated herein, preferably, the present invention isparticularly beneficial to the formation of gate dielectrics, however,other applications may also benefit therefrom.

What is claimed is:
 1. A system for use in the fabrication of a gatestructure, the apparatus comprising: a vacuum chamber includingsubstrate assembly holder adapted to hold a substrate assembly having asurface; an ozonizer apparatus, the ozonizer apparatus comprising: anozone source, and an ozonizer structure proximate the surface of thesubstrate assembly in the vacuum chamber, the ozonizer structure havingopenings adapted to direct ozone towards the surface of the substrateassembly; an evaporation apparatus, the evaporation apparatuscomprising: a metal oxide source, and an electron beam generation deviceoperable to generate an electron beam that impinges on the metal oxidesource to evaporate metal oxide of the metal oxide source for formationof metal oxide on the surface of the substrate assembly; and an ion beamapparatus, the ion beam apparatus comprising: an inert gas sourceoperable to provide an inert gas, and an ion gun operable to generate anion beam using the inert gas and directing the ion beam for contact atthe surface of the substrate assembly.
 2. The system of claim 1, whereinthe metal oxide source includes a high purity source material, whereinthe high purity source material has a purity that is about. 99.999% orgreater.
 3. The system of claim 2, wherein the metal oxide sourceincludes material selected from the group consisting of TiO₂, Y₂O₃,Al₂O₃, ZrO₂, HfO₂, Y₂O₃—ZrO₂, ZrSiO₄, LaAlO₃, and MgAl₂O₄.
 4. The systemof claim 3, wherein the metal oxide source is a TiO₂ source.
 5. Thesystem of claim 1, wherein the ion beam apparatus further comprises acontroller operable to delay generation of the ion beam until at least amonolayer of metal oxide is formed using the evaporation apparatus. 6.The system of claim 1, wherein the ozonizer structure is a ringstructure having openings adapted to direct ozone uniformly towards thesubstrate assembly surface.
 7. The system of claim 1, wherein theevaporation apparatus further comprises an evaporator controlleroperable to control the electron beam power such that a deposition ratefor metal oxide formation on the surface of the substrate assembly isabout 0.1 nm/second to about 0.2 nm/second.
 8. The system of claim 1,wherein the ion beam apparatus further comprises an ion beam controlleroperable to control ion beam density of the ion beam such that the ionbeam density is in the range of about 0.5 ma/cm² to about 1 ma/cm². 9.The system of claim 1, wherein the ion beam source includes a gasselected from a group consisting of argon, xenon, and krypton.
 10. Thesystem of claim 1, wherein the system further comprises a heating deviceoperable to heat the substrate assembly within the range of about 100°C. to about 150° C.